Conventionally, a rotary-type fluid machine has been used as a fluid machine for compressing or expanding a working fluid such as represented by a refrigerant. Because of its compactness and simple structure, the rotary-type compressor has been used widely for electric appliances, such as air-conditioners, water heaters, and refrigerator-freezers. A configuration of the rotary-type compressor is disclosed in, for example, “Refrigerating and Air Conditioning Handbook, New Edition Fifth Edition, Vol. II, Equipment (Japanese Association of Refrigeration, 1993, pp. 30-43)”. The following describes the configuration of the conventional rotary-type compressor with reference to FIG. 7. FIG. 7 is a vertical cross-sectional view illustrating the conventional rotary-type compressor.
A rotary-type compressor 120 shown in FIG. 7 includes a closed casing 101, a compression mechanism 122 provided in a lower portion of the closed casing 101, and an electric motor 124 provided above the compression mechanism 122. The compression mechanism 122 includes a shaft 102 having an eccentric portion 102a, a cylinder 103, a roller 104, a vane 105, a spring 106, an upper bearing member 107 having a discharge port 107a, and a lower bearing member 108. The motor 124 includes a stator 109 and a rotor 110 fixed to the shaft 102.
A suction pipe 111 and a discharge pipe 112 are connected to the closed casing 101. An oil reservoir 113 is formed in a bottom portion of the closed casing 101 by accumulating oil, whereby the surrounding region of the compression mechanism 122 is filled with the oil. At the top of the closed casing 101, a terminal 114 for supplying electric power to the motor 124 from the outside extends through the closed casing 101.
The operation of the rotary-type compressor 120 having the above-described configuration is described below.
When electric current passes through the terminal 114 to the motor 124 and the rotor 110 rotates, the roller 104 undergoes eccentric rotational motion by the action of the eccentric portion 102a. As a result, the refrigerant is sucked from the suction pipe 111 and a suction port 103a, and compressed in a compression chamber 115. The compressed refrigerant blows out into the internal space of the closed casing 101 through the discharge port 107a. The refrigerant blown out into the closed casing 101 is discharged from the discharge pipe 112 toward a radiator.
Here, the sliding operation of the cylinder 103 and the vane 105 during the period in which the rotary-type compressor 120 is performing the compression operation is described below.
The cylinder 103, the roller 104, the vane 105, the upper bearing member 107, and the lower bearing member 108 form two compression chambers 115a, 115b. Two compression chambers 115a and 115b include the compression chamber 115a communicating with the suction port 103a on the suction stroke, and the compression chamber 115b communicating with the discharge port 107a on the compression/discharge stroke. The compression chamber 115a on the suction stroke is filled with the refrigerant at a suction pressure (low pressure). The compression chamber 115b on the compression/discharge stroke is filled with the refrigerant at an intermediate pressure that is between the suction pressure (low pressure) and a discharge pressure (high pressure) when in the compression stroke, or is filled with the refrigerant at the same discharge pressure (high pressure) as that in the closed casing 101 when in the discharge stroke after the compression has finished. As a result, in the cylinder 103, there exists a region with a suction pressure (low pressure) and a region with an intermediate pressure or a discharge pressure (high pressure), and there is a portion with a lower pressure than a discharge pressure (high pressure) of the refrigerant filled in the closed casing 101.
Accordingly, oil is supplied directly from the oil reservoir 113 to sliding portions of the cylinder 103 and the vane 105 because of the pressure difference between the interior of the closed casing 101 and the interior of the cylinder 103. The oil flows toward the interior of the cylinder 103, lubricating the whole sliding surfaces.
The rotary-type fluid machine is also useful as an expander. Because of its compactness and simple structure, use of the rotary-type expander in place of an expansion valve has been studied for recovering the energy of expansion of the refrigerant during the process of decompressing a high-pressure refrigerant. An example of the configuration of such a rotary-type expander is a fluid machine in which a rotary-type compression mechanism and a rotary-type expansion mechanism are constructed integrally, as disclosed in JP 2005-106046A and JP 2005-106064A. This kind of fluid machine often is referred to as an expander-compressor unit.
The configuration of the fluid machine disclosed in JP 2005-106046A and JP 2005-106064A will be described below with reference to the vertical cross-sectional view of FIG. 8.
A fluid machine 200 shown in FIG. 8 includes a closed casing 201, a compression mechanism 202, a motor 203, a rotary-type expansion mechanism 204, a shaft 205, and an oil reservoir 206. The compression mechanism 202 is provided in a lower portion of the closed casing 201. The rotary-type expansion mechanism 204 is provided above the motor 203. The shaft 205 couples the compression mechanism 202, the motor 203, and the expansion mechanism 204 to each other. The oil reservoir 206 is provided in a bottom portion of the closed casing 201, for filling the circumference of the compression mechanism 202 with oil.
The operation of the fluid machine 200 having the above-described configuration is described below.
When electric current is passed to the motor 203, mechanical power is generated at the motor 203. The mechanical power is transmitted to the compression mechanism 202 by the shaft 205. The compression mechanism 202 sucks and compresses the refrigerant discharged from an evaporator, and discharges the compressed refrigerant to the interior of the closed casing 201. The refrigerant discharged to the interior of the closed casing 201 then is discharged toward a radiator. The refrigerant cooled by the radiator is guided to the expansion mechanism 204 and is expanded at the expansion mechanism 204, while the energy of expansion there is being recovered as mechanical power. Then, the refrigerant after the expansion is heated by the evaporator and is again sucked into the compression mechanism 202.
In the fluid machine 200 with the just-described configuration, the expansion mechanism 204, the motor 203, and the compression mechanism 202 are aligned in that order from the top to the bottom. Since the compression mechanism 202 is immersed in oil, as in the case of the conventional rotary-type compressor (FIG. 7), sliding portions of the cylinder and the vane are lubricated by the same principle as described previously.